Forming tool

ABSTRACT

The invention relates to a forming tool for forming sheet blanks in a diaphragm press of the kind comprising an openable, closed pressure chamber, which is divided in a gas and liquid tight manner by means of a flexible diaphragm. The forming tool is arranged on one side of the diaphragm and a sheet blank to be formed is arranged between the forming tool and the diaphragm. The opposite side of the diaphragm is pressurized by a fluid being supplied at high pressure to cause the flexible diaphragm to deform and, thus, the sheet blank to be pressed against the forming tool. The forming tool comprises an elongate cutting and flanging tool along at least part of its periphery and/or around an intended opening in the sheet blank.

The present invention relates to a forming tool for forming sheet blanksin a diaphragm press of the kind comprising an openable, closed pressurechamber, which is divided in a gas and liquid tight manner by means of aflexible diaphragm, the forming tool being adapted to be arranged on oneside of the diaphragm and a sheet blank to be formed being adapted to bearranged between the forming tool and the diaphragm, while the oppositeside of the diaphragm is adapted to be pressurised by a fluid beingsupplied at high pressure to cause the flexible diaphragm to deform and,thus, the sheet blank to be pressed against the forming tool, theforming tool further comprising a cutting edge, so that the sheet blankis both formed into the desired shape and cut to the desired size in asingle forming step.

BACKGROUND ART

In connection with forming sheet blanks, such as sheets of steel oraluminium for use in vehicles, it is known to use so-called diaphragmpresses of the kind described above. In such a press, a forming tool isprovided in a closed press chamber and the sheet blank to be formed isarranged between the forming tool and an elastic diaphragm of rubber ora polymer, which divides the press chamber in two separate chamberportions in a gas and liquid tight manner. By supplying a liquid at highpressure at the opposite side of the diaphragm, the diaphragm will bedeformed and press the sheet blank against the forming tool whereby theblank obtains the desired shape. Forming using diaphragm presses of thiskind is particularly advantageous in conjunction with relatively smallproduction runs, since the cost of manufacturing the forming tools isrelatively low.

However, in forming operations using a diaphragm press, as in everyother kind of forming operation, it is desirable that, to the utmostpossible extent, the blank be formed into a finished product in onesingle forming step, thereby avoiding, as far as possible, anysubsequent machining that would increase the costs. Thus, it isdesirable that, in the forming operation, the blank be cut to thecorrect size and shape and that, if desired, flanged edges be formed,said flanged edges being used, for example, for attaching the finishedblank and for connecting it to other structural elements of the endproduct, such as a vehicle.

EP 0 288 705 discloses a forming tool for diaphragm presses by means ofwhich it is possible to cut the sheet-metal blank to the desired sizeand to form a flanged edge along the periphery of the cut sheet-metalblank. This is achieved by the forming tool having cutting bars with asharp cutting edge along the circumference of the forming tool andrecesses for forming the flanged edges after cutting. During the formingprocess, the sheet-metal blank will, at a certain degree of deformation,be pressed against the cutting edges, which will cause the sheet torupture and be cut off to the predetermined size, flanged edges beingthen formed at the cut-off edge portions by said portions being pressedinto the recesses provided therefor in the forming tool. One drawback ofthis forming tool is, however, that the sheet-metal blank has to bedeformed over a very long distance before it reaches the cutting edgeand is cut off, which has a negative effect on the dimensional accuracyand other quality aspects. In addition, it is often desirable toprestretch the sheet-metal blank in one direction to the yield point ofthe material, preferably 3–6% beyond the yield point, before the formingoperation in order to avoid elastic springback of the sheet-metal blankafter forming. This implies a lateral contraction of the sheet-metalblank in the other direction, and in the case where there are largerecesses, for example for the purpose of forming flanged edges, parallelto the stretching direction, the sheet-metal blank will be deformed bysaid recesses, which results in a product of inferior quality.

BRIEF SUMMARY OF THE INVENTION

The present invention aims at providing an improved forming tool fordiaphragm presses, which allows the sheet blank to be cut to the desiredsize and a flanged edge to be formed by bending along at least part ofthe periphery of the sheet-shaped blank and/or along a circumferentialedge of an opening therein in a single forming step, while ensuring ahigh degree of dimensional accuracy and shape permanence as well as afinished product of high quality. An additional advantage obtained bymeans of the forming tool according to the invention is that it iseasier to remove both the formed product and the remaining surplus orscrap after the forming operation. At least said objects and advantagesare obtained by means of a forming tool according to claim 1.

The invention is thus based on the understanding that the above objectsand advantages are obtained if the forming tool, in the places where thesheet blank is to be cut and bent to form a flanged edge, is providedwith an elongate cutting and flanging tool, which is displaceable withthe aid of actuating means towards and away from the diaphragm in a slotin the forming tool. In one typical embodiment, the forming tool cancomprise, as shown and described also in connection with the followingworking examples, such a cutting and flanging tool for the purpose ofcutting the sheet-metal blank and bending it to form a flanged edgealong the whole periphery of the blank. One example of such anapplication is car body panels in the form of, for example, a car hoodor a car roof. However, a cutting and flanging tool could also beadapted to cut the blank and bend it to form a flanged edge along thecircumference of an opening therein, for example for the purpose offorming window and ventilation openings in car body panels. It wouldalso be conceivable to form a flanged edge by cutting and bending alongonly part of a body panel edge or a circumferential edge of an openingin the blank. In such cases, the cutting and flanging tool does not needto extend continuously in a closed loop, but may be arranged along alimited section having a beginning and an end.

Preferably, the cutting and flanging tool is, in an initial position,flush with the forming surface. The cutting function is achieved by thecutting and flanging tool being provided with a sharp shoulder edge,which serves as a cutting edge and which, conveniently, can have aheight 1–3 times the thickness of the sheet blank to be formed. When asufficiently high pressing pressure has been reached, the blank is cutalong said edge, the cutting thus being effected before the blank hasbeen deformed to a significant degree. Owing to the small depth of therecess, its negative influence on the blank, perpendicularly to thelateral contraction, in connection with any prestretching will beinsignificant. Moreover, by arranging the cutting edge on the cuttingand flanging tool, it is easy to provide a flanged edge of varying widthby forming the cutting edge at different distances from the edge of thecutting and flanging tool that is oriented towards the forming surfaceof the forming tool against which the blank is formed.

The cutting and flanging tool is moved towards and away form thediaphragm with the aid of an arbitrary type of actuating means. In thepreferred embodiment, the actuating means is formed of a plurality ofhydraulically operated pistons arranged at intervals of about 100 mm.However, other types of actuating means are also conceivable. At lowpressures, pneumatic pistons could be used, for instance.

In the preferred embodiment, the inward displacement of the cutting andflanging tool is controlled by the pressing pressure being exerted, byway of the diaphragm, on a release valve, which, when the pressure ishigh enough, is pressed inwards and actuates a valve body, which drainsthe hydraulic system of the pistons, thus allowing the cutting andflanging tool to be forced inwards by the pressing pressure exertedthereon. In this way, the diaphragm will press the edge portion of thecut blank into the slot in the cutting and flanging tool, so that saidedge portion will form an inwardly bent flanged edge. After a possiblefurther pressure increase aiming at a final forming of the blank, thepressure in the pressure chamber is released and the press can then beopened. By the position of the cutting and flanging tool in the slotbeing controllable with the aid of one or more actuating means, both thefinished product and the cut-off scrap can be easily disengaged from theforming tool by the actuating means being caused to displace the cuttingand flanging tool outwards. The cutting and flanging tool will thusdisengage the finished product and the scrap and press them out of theforming tool. In many cases, the product and the scrap will stick firmlyto the forming tool.

In the following working example, one embodiment of the forming tool forforming car body panels will be described. It will be appreciated,however, that the forming tool according to the invention can also beused for forming other sheet blanks.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The drawings show, by way of example, one embodiment of the invention.

FIG. 1 is a cross section through a diaphragm press with a forming toolaccording to the invention arranged therein for forming car body panels.

FIG. 2 is a top view of the bottom tray of the diaphragm press in FIG.1.

FIGS. 3–6 are schematic partial cross sections through the cutting andflanging tool and a release valve of the forming tool according to theinvention at different pressing pressure levels.

FIGS. 7 and 8 are partial cross sections similar to those in FIGS. 3–6,which illustrate the function of the release valve in greater detail.

FIG. 9 is a pressure/time chart illustrating the pressure levels duringdifferent time intervals of a forming cycle.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

In the following, an embodiment will be described in which the formingtool is used for forming sheet-metal blanks for the automotive industry.

FIG. 1 is a cross section through a diaphragm press 1. The latterincludes a bottom tray 2 and an upper part 3, which, when broughttogether as shown in the figure, define a closed pressure chamber 4. Aflexible diaphragm 5 is arranged between the bottom tray 2 and the upperpart 3, which diaphragm provides a gas and liquid tight shield betweenthe bottom tray 2 and the upper part 3.

A forming tool 6 according to the invention having an annular cuttingand flanging tool 7 is arranged in the bottom tray. Edge elements 8 withschematically illustrated stretching means 9, 9′ are provided betweenthe forming tool 6 and the side walls of the bottom tray 2, and both theforming tool and the edge elements 8 rest on a bottom plate 10.

In connection with forming using the diaphragm press shown, asheet-metal blank 11 to be formed is arranged between the forming tool 6and the diaphragm 5, two opposite side edges thereof being inserted inthe stretching means 9, 9′, as shown in FIG. 1. The stretching means 9,9′ allow the sheet-metal blank to be prestretched in one direction tothe yield point of the material, or preferably slightly beyond the yieldpoint. An excess pressure is then applied in the press chamber 4 on theupper side of the diaphragm 5 by a liquid, preferably oil, beingsupplied at high pressure by means of a schematically illustrated pump12 from a storage tank 13. Since the pressure on the upper side of thediaphragm 5 is increased, the latter will be pressed against thesheet-metal blank 11 and the forming tool 6, the shape of whose upperside corresponds to the desired shape of the formed end product.

FIG. 2 is a schematic top view of the bottom tray 2 with a forming tool6 arranged therein. The forming tool shown in the figure is intended forforming sheet-metal blanks into car hoods and the annular cutting andflanging tool 7 extends along the peripheral edges of the car hood to beformed. A release valve 14, which is schematically illustrated in thelower left corner of the figure, will be described in more detail below.

Reference is now made to FIGS. 3–6, which illustrate the function of theforming tool according to the invention and, in particular, the functionof the forming tool's cutting and flanging tool 7. The latter isarranged in a slot in the forming tool and its outer surface has ashoulder-shaped cross section achieved by a recess 15 being made alongan edge of the cutting and flanging tool 7, said recess being locatedclosest to the forming surface 16 against which the sheet-metal blank 11is to be formed. A cutting edge 17 is formed between the outer-mostouter surface of the cutting and flanging tool 7 and said recess 15. Inthe example shown, the recess 15 has a rectangular cross section.However, it could also have, for example, a wedge-shaped cross section,so that the end of the recess located closest to the forming surface 16is flush with the forming surface. Thus, the negative influence of therecess on the sheet-metal blank in connection with the lateralcontraction mentioned above during prestretching of the sheet-metalblank would be even further reduced. The cutting and flanging tool 7 isoperable by means of a plurality of hydraulic cylinders 18 provided atintervals of about 100 mm along the whole circumference of the cuttingand flanging tool 7.

The figures also show the release valve 14, the outer surface of whichis located slightly within the outer surface of the forming tool. Therelease valve 14 is spring-loaded towards the exterior by means of cupsprings 19 and the innermost end of the release valve comprises a valvebody 20, which is capable of closing and opening a passage in ahydraulic pipe 21.

In an initial position, as shown in FIG. 3, the sheet-metal blank 11 isstretched with the aid of the stretching means 9, 9′, the cutting andflanging tool 7 is pressed outwards by a hydraulic pressure in thehydraulic cylinders 18 in such manner that the outermost surface of thecutting and flanging tool is flush with the forming surface 16, and thehydraulic pipe 21 is closed by the release valve 14 being pressedoutwards by the spring 19. However, at this stage, no pressure has yetbeen applied to the outside of the diaphragm 5 and the sheet-metal blank11 thus extends, not yet formed or cut, past both the cutting andflanging tool 7 and the release valve 14.

In FIG. 4, a pressure has been applied to the outside of the diaphragm 5causing it to be pressed against the sheet-metal blank 11, and thepressure is high enough for a hole to have been stamped in thesheet-metal blank 11 along the periphery of a hole in which the releasevalve 14 is disposed. However, the force of the spring 19 is so greatthat the passage in the hydraulic pipe 21 remains closed.

In FIG. 5, the pressure has increased further, which has caused thesheet-metal blank 11 to be cut along the cutting edge 17 of the cuttingand flanging tool 7. The passage in the hydraulic pipe 21 is, however,still closed.

In FIG. 6, the pressure has increased even further, so that it, by wayof the diaphragm 5, overcomes the spring force of the spring 19, and therelease valve has been displaced inwards in such manner that the passagein the hydraulic pipe 21 has been opened. The hydraulic liquid is thusdrained from the hydraulic pistons 18 and the cutting and flanging tool7 is displaced into the forming tool. The diaphragm 5 will thus form aflanged edge 22 by bending along the periphery of the part of the cutsheet-metal blank 11 that is located above the forming surface 16 andthat will form the finished product.

In the schematic cross sections 7 and 8, the function of the releasevalve 14 is shown in more detail. In FIG. 7, which corresponds to FIG.3, the forming tool 6 is in an initial position, the sheet-metal blank11 being stretched over it with the aid of the stretching means 9, 9′. Apump 23 is used to generate a pressure in a hydraulic pipe 24, whichextends through the bottom plate 10 to each of the hydraulic cylinders18, such that the cutting and flanging tool 7 is displaced upwards andits outer-most surface is flush with the forming surface 16 of theforming tool. The pressure in the pipe 24 is maintained by means of acheck valve 25 and as long as the passage in the pipe 21, whichcommunicates with the pipe 24, is closed by the valve body 20 owing tothe fact that the release valve 14 is pressed outwards by the spring 19,no hydraulic liquid can be evacuated there either.

In FIG. 8, which corresponds to FIG. 6, the diaphragm (not shown in thisfigure) has pressed the release valve 14 down, so that the passage inthe pipe 21 is open. This allows hydraulic liquid to be evacuatedthrough the pipe 21 and the pressure in the hydraulic cylinders 18 to bereleased. The diaphragm then causes an inward displacement of thecutting and flanging tool 7 and the flanged edge 22 is bent along theperiphery of the sheet-metal blank.

After the forming operation has been completed, when the pressure hasbeen released from the press chamber 4 and the upper part 3 of the pressas well as the diaphragm 5 have been removed, the release valve 14 willreturn to its initial projecting position, thus causing the passage inthe hydraulic pipe 21 to close. By generating once more, at this stage,a hydraulic pressure in the pipe 24, the hydraulic cylinders 18 willcause an outward displacement of the cutting and flanging tool 7 andboth the finished product and the remaining scrap will be displacedoutwards and disengaged from the forming tool.

FIG. 9 shows a pressure/time chart illustrating the pressure in thepress chamber during different time intervals of the forming operation.At A the sheet-metal blank 11 is stretched with the aid of thestretching means 9, 9′ to the yield point of the material. The presschamber is then pressurised in such manner that the diaphragm 5 ispressed against the sheet-metal blank 11 and the forming tool, and at Bthe hole is cut out above the release valve 14. During a continuedpressure increase, point C is reached, at which the sheet-metal blank iscut along the cutting edge 17 of the cutting and flanging tool 7. With afurther pressure increase point C is reached, at which the release valve14 is pressed inwards by the diaphragm, so that he hydraulic pistons 18are drained. This causes the cutting and flanging tool 7 to be displacedinwards and the flanged edge 22 to be formed by bending along theperiphery of the cut sheet-metal blank. The pressure is then increasedslightly more to point E in order to further reinforce and define theshape of the sheet-metal blank on the forming tool. Finally, thepressure in the press chamber is released and drops to atmosphericpressure, as illustrated by the curve section F. The cut, flanged andformed product can then be removed from the press to be furtherprocessed.

1. A forming tool for forming sheet blanks in a diaphragm press of thekind comprising an openable, closed pressure chamber, which is dividedin a gas and liquid tight manner by means of a flexible diaphragm, theforming tool being adapted to be arranged on one side of the diaphragmand a sheet blank to be formed being adapted to be arranged between theforming tool and the diaphragm, while the opposite side of the diaphragmis adapted to be pressurized by a fluid being supplied at high pressureto cause the flexible diaphragm to deform and, thus, the sheet blank tobe pressed against the forming tool, the forming tool comprising: acutting edge, so that the sheet blank is both formed into the desiredshape and cut to the desired size in a single forming step; and anelongate cutting and flanging tool along at least part of its peripheryand/or around an intended opening in the sheet blank, the cutting andflanging tool having a cutting edge and being displaceable, with the aidof actuating means, in an elongate slot in the forming tool towards andaway from the diaphragm, in such manner that, at a first pressingpressure, the sheet blank is caused to be cut off against the cuttingedge and, as the pressure is continuously increased, the cutting andflanging tool is caused to be displaced into the slot in the formingtool away from the diaphragm, so that the peripheral edge of the sheetblank and/or the circumferential edge around an opening therein is/aredeformed towards the interior of the slot during forming of a flangededge in the sheet blank.
 2. The forming tool as claimed in claim 1,wherein the actuating means comprises a plurality of hydraulic cylindersalong the longitudinal extent of the cutting and flanging tool.
 3. Theforming tool as claimed in claim 1, wherein the cutting edge of thecutting and flanging tool is formed by a recess along a longitudinaledge of the cutting and flanging tool that is oriented towards a formingsurface of the forming tool, the width of the recess corresponding tothe width of the flanged edge to be formed.
 4. The forming tool asclaimed in claim 3, wherein the recess of the cutting and flanging toolhas a varying width along its longitudinal extent so as to form aflanged edge of varying width.
 5. The forming tool as claimed in claim1, wherein, in an initial, projecting position, an outermost surface ofthe cutting and flanging tool is flush with a forming surface of theforming tool.
 6. A diaphragm press comprising an openable, closedpressure chamber, which is divided in a gas and liquid tight manner bymeans of a flexible diaphragm, and a forming tool, wherein the formingtool is adapted to be arranged on one side of the diaphragm and a sheetblank to be formed being adapted to be arranged between the forming tooland the diaphragm, while the opposite side of the diaphragm is adaptedto be pressurized by a fluid being supplied at high pressure to causethe flexible diaphragm to deform and, thus, the sheet blank to bepressed against the forming tool, the forming tool comprising: a cuttingedge, so that the sheet blank is both formed into the desired shape andcut to the desired size in a single forming step; and an elongatecutting and flanging tool along at least part of its periphery and/oraround an intended opening in the sheet blank, the cutting and flangingtool having a cutting edge and being displaceable, with the aid ofactuating means, in an elongate slot in the forming tool towards andaway from the diaphragm, in such manner that, at a first pressingpressure, the sheet blank is caused to be cut off against the cuttingedge and, as the pressure is continuously increased, the cutting andflanging tool is caused to be displaced into the slot in the formingtool away from the diaphragm, so that the peripheral edge of the sheetblank and/or the circumferential edge around an opening therein is/aredeformed towards the interior of the slot during forming of a flangededge in the sheet blank.